It is known that acrylonitrile can be produced from propylene in various processes in which propylene is brought into contact with molecular oxygen and ammonia in a gas phase in the presence of a catalyst at an elevated temperature. These processes are known as catalytical ammoxidation processes for propylene. This ammoxidation of propylene can be effected only in the presence of a catalyst. U.S. Pat. No. 2,904,580 disclosed, for the first time, a P--Mo--Bi--O type catalyst effective for the ammoxidation of propylene. After this U.S. patent, various types of catalysts were provided for the ammoxidation process for propylene. For example, U.S. Pat. No. 3,766,092 discloses an Mo--Bi--Fe--Co--Na and/or K--P--O type ammoxidation catalyst; British Patent No. 1,319,190 discloses an [(Ni and/or Co)--(As and/or P)--Fe--Bi--Mo--(Alkalimetal, Ta, Nb and/or rare earth metal)--O] type ammoxidation catalyst; U.S. Pat. No. 4,123,453 discloses an [(alkali metal)--(Ni and/or Co)--(As and/or P)--(at least one element selected from Groups IIA and IIB in the Periodic Table)--Fe--Bi--Mo--O] type ammoxidation catalyst; British Pat. No. 1,478,621 discloses an X--(A)--C--Fe--Bi--Mo--O type ammoxidation catalyst in which X denotes at least one member selected from the group consisting of Ge, Sn, Cu, Ag, Cr, Ru, W, Be, B, Ga, In, Mn, Sb, Th, Zr and Y, A denotes at least one element selected from the group consisting of alkali metals, alkaline earth metals, rare earth elements, Nb, Ta, Tl, P and As and C represents at least one element selected from the group consisting of Co, Mg, Zn, Cd and Ca, and; U.S. Pat. No. 3,872,148 discloses a [Bi--Mo--W--(at least one element selected from Group II in the Periodic Table)--(at least one element selected from the group consisting of Ti, Zr, Nb, Ta, V, Cr, Mn, Fe, Co and Ni)--O] type ammoxidation catalyst.
Some of the above-mentioned conventional ammoxidation catalysts are effective for producing acrylonitrile with a high yield. However, almost all of the conventional ammoxidation catalysts are industrially unsatisfactory due to their poor resistance to attrition. It is essential that industrially usable catalysts exhibit a high resistance to attrition.
In order to enhance the resistance of the catalyst to attrition, it is effective to utilize a carrier consisting of for example, silica. However, usually, the utilization of a carrier results in a remarkable decrease in the yield of acrylonitrile. That is, when a carrier is used in such an amount that the resistance of the catalyst to attrition is considerably enhanced, the yield of acrylonitrile is significantly reduced.
When a conventional catalyst, which is effective for producing acrylonitrile with a high yield but which exhibits a poor resistance to attrition, is used in a fixed bed type reactor, the charging operation of the catalyst into the reactor causes the catalyst to be abraded and pulverized. The pulverized catalyst particles hinder the flow of reaction gases through the reactor. This hindering results in an undesirable increase in the pressure drop through the reactor and in side-reactions.
Also, when a conventional catalyst is used in a fluidized bed type reactor, during the ammoxidation reaction, the catalyst is abraded and pulverized during the time the reaction is taking place. A portion of the pulverized catalyst particles flow out with the reaction gases from the reactor. The loss of the catalyst from the reactor causes the fluidized bed reaction to become unstable and the life of the catalyst to be shortened. In this case, accordingly, it is necessary to feed an additional amount of the catalyst to the reactor, which additional amount corresponds to the loss of the catalyst. Therefore, the yield of acrylonitrile per unit amount of the catalyst decreases.
Accordingly, it is strongly desired to provide an ammoxidation catalyst which is effective for producing acrylonitrile with a high degree of selectivity to acrylonitrile with a high yield of acrylonitrile and which exhibits excellent resistance to attrition. Furthermore, in order to reduce the cost of the catalyst, it is desired that, even when the catalyst is borne on a large amount of the carrier, the catalyst is capable of producing acrylonitrile with a high yield at a relatively low temperature in a relatively short contact time.